1. Field of the Invention
This invention relates to a constant-rate discharge valve and an electronic automatic sphygmomanometer using such a discharge valve.
2. Description of the Prior Art
Conventionally, a manual sphygmomanometer is provided with a constant-rate discharge valve. Such a valve is provided at the entrance of a rubber bulb for inflating a cuff, and the cuff is deflated at a constant rate by manually adjusting a regulating valve.
In order to measure blood pressure using such a manual sphygmomanometer, first the cuff pressure is raised to a value above systolic blood pressure, after which the cuff pressure is adjusted manually by the regulating valve to deflate the cuff at a constant rate. During this deflation, systolic and diastolic blood pressure are measured by detecting Korotkoff sounds.
In an electronic automatic sphygmomanometer, the constant-rate discharge valve cannot be manually adjusted. For this reason, the constant-rate discharge valve used is so adapted that the cuff is deflated at a constant rate.
FIG. 4A is a front view of a conventional constant-rate discharge valve, and FIG. 4B is a side view of the conventional constant-rate discharge valve. These views show a typical arrangement of a constant-rate discharge valve employed in an electronic automatic sphygmomanometer. With reference to FIGS. 4A and 4B, there is shown a constant-rate discharge valve main body 100 having one end open to the atmosphere and another end formed into a hollow cylindrical member penetrated by a small orifice 101. The valve is fitted into a pipe T indicated by the slanting lines.
As for the operation of the constant-rate valve thus constructed, air which is passed through the interior of the pipe T is discharged at a constant rate by passing through the orifice 101.
Thus, the constant-rate discharge valve of the manual sphygmomanometer involves difficulty in terms of operation, as mentioned above. Though the constant-rate discharge valve of the fully automatic sphygmomanometer constructed as described above eliminates this difficulty, it is difficult to maintain the precisely machined state of the orifice, and therefore disparities in dimensions and shape arise. As a result, it is difficult to maintain a constant discharge state without variance.
Another problem is that the amount of discharged air cannot be adjusted with the fully automatic sphygmomanometer constructed as described above.